Process for comminuting fluorescent whitening agents and compositions obtained thereby

ABSTRACT

A PROCESS FOR COMMINUTING RELATIVELY LARGE CRYSTALS OF SOLID FLUORESCENT WHITENING AGENTS TO A PARTICLE SIZE HAVING A DIAMETER NO GREATER THAN 5 MICRONS WHICH COMPRISES GRINDING A WATER-WET PRESSCAKE OF SAID AGENT WITH AT LEAST ONE MOLECULAR EQUIVALENT OF ANHYDROUS SODIUM SULFATE FOR EACH TEN MOLECULAR EQUIVALENTS OF WATER PRESENT IN THE PRESSCAKE AND THE FLUORESCENT WHITENING COMPOSITIONS OBTAINED THEREBY.

United States Patent PROCESS FOR COMMINU'IING FLUORESCENT WHITENING AGENTS AND COMPOSITIONS OB- TAINED THEREBY Theodore A. Langstroth, Cincinnati, Ohio, assignor to Sterling Drug Inc., New York, N.Y.

No Drawing. Continuation-impart of abandoned application Ser. No. 839,703, July 7, 1969. This application Nov. 22, 1971, Ser. No. 201,198

Int. Cl. D06l'3/12 U.S. Cl. 252301.3 W 4 Claims ABSTRACT OF THE DISCLOSURE A process for comminuting relatively large crystals of solid fluorescent whitening agents to a particle size having a diameter no greater than 5 microns which comprises grinding a water-wet presscake of said agent with at least one molecular equivalent of anhydrous sodium sulfate for each ten molecular equivalents of water present in the presscake and the fluorescent whitening compositions ob tained thereby.

This application is a continuation-in-part of my prior copending United States patent application Ser. No. 839,703, filed July 7, 1969, now abandoned.

This invention relates to a process for grinding solid particulate materials and to compositions of matter so obtained. More particularly, the invention relates to a process for comminuting solid fluorescent whitening agents and to articles of manufacture comprising solid fluorescent whitening agent compositions useful for incorporation into detergents.

Solid detergent compositions today universally contain fluorescent whitening agents, also called optical bleaches or optical brighteners. In general, the fluorescent whitening agents are amorphous or preferably crystalline solid organic compounds which are reasonably water-soluble by virtue of the presence in the molecule of one or more water-solubilizing substituents, for example the sulfonate anion and/or amine substituents. The compounds are ideally white, but in practice they are generally creamcolored to yellowish powders, depending upon the nature of the compound itself, the form in which it exists (amorphous or crystalline, and the nature of the crystalline form) and the manner in which it is isolated and dried. Furthermore, a number of fluorescent whitening agents are rather sensitive to heat, and tend to turn yellow during the drying of the presscake unless a low temperature is maintained. Moreover, certain fluorescent whitening agents, for reasons which are not fully understood, tend to turn yellow in color when ground to very fine particle size. The yellow color imparted to the whitening agents by the above-mentioned processes makes them less desirable for incorporation into white detergents because of the yellowish tint which may result in the detergent composition.

It is an object of the present invention to provide an effective method for comminuting relatively large crystals of a substantially white fluorescent whitening agent without undue yellowing of its color. It is another object of .this invention to provide an eflicient method for removing the excess water from presscake of fluorescent whitening agents without subjecting the fluorescent whitening agent to high drying temperatures. It is yet another object of this invention to provide an eifective method for simultaneously drying and grinding a relatively white fluorescent whitening agent without substantially yellowing the color of the product. And it is a further objects of this invention to provide a novel fluorescent whitening agent composition consisting of finely-comminuted fluorescent whitening agent and a compatible, inert diluent in the form of a free-flowing powder.

In the first of its process aspects, this invention resides in a process for treating a presscake consisting essentially of water and relatively large crystals of a fluorescent whitening agent, which comprises grinding said presscake at a temperature of 20 to 60 C. in the presence of at least one and up to eight molecular equivalents of anhydrous sodium sulfate for each ten molecular equivalents of water in said presscake until substantially all of said crystals are reduced to a diameter of less than approximately five microns.

In a second process aspect, this invention resides in a process which comprises drying the product of the first process aspect above-described to remove some or all of the moisture content.

In one of its composition aspects, the invention resides in an article of manufacture which comprises a relatively white fluorescent whitening agent in crystalline solid form having an average particle size less than approximately five microns in diameter and, in admixture therewith, crystalline sodium sulfate, decahydrate.

In a second of its composition aspects, the invention resides in an article of manufacture which comprises a fluorescent whitening composition obtained in accordance with the second aspect of this invention and having a moisture content of less than two precent consisting essentially of a crystalline fluoroscent whitening agent having a particle size less than approximately five microns and, in admixture therewith, anhydrous sodium sulfate.

In a third composition aspect, the invention resides in an article of manufacture prepared in accordance with the first process aspect of this invention, which comprises a solid, particulate fluorescent whitening agent having a particle size less than approximately five microns in diameter (that is, in their largest dimension) and, in admixture therewith, crystalline sodium sulfate decahydrate.

In accordance with the first process aspect of this invention a solid, crystalline fluorescent whitening agent in the form of a presscake, containing essentially only water and the fluorescent whitening agent, is admixed with anhydrous sodium sulfate and the mixture is ground by one or more of a number of grinding processes known to the art. The quantity of anhydrous sodium sulfate used depends chiefly on the amount of water present in the presscake and the particular active concentration of fluorescent Whitening agent desired in the final composition. However, there must be used as a minimal quantity at least a suflicient amount of anhydrous sodium sulfate to interact completely with the water contained in the presscake for the formation of sodium sulfate decahydrate (Glaubers Salt). Thus, as a minimal amount, at least approximately one molecular equivalent of anhydrous sodium sulfate is used for each ten molecular equivalents of Water in the presscake, as determined by routine analytical procedures.

Larger amounts of anhydrous sodium sulfate are used when it is desired to obtain a particular cut or concentration of active whitening agent in the composition. With regard to this aspect of the invention, I have found that when compositions in which the concentration of fluorescent Whitening agent ranges from about twenty to about eighty percent are used in the proper amount to produce equal concentrations of whitening agent, substantially equivalent qualities of Whitening effect, solubility and color effect in detergents are obtained. However, for practical use, I prefer to obtain compositions which have an active fluorescent brightening concentration in the range of approximately 35 to 70 percent.

The water-wet presscake of fluorescent whitening agent can also have a wide range in the ratio of solids to water, for example from about 40 to percent of solids. However, I prefer to use those water-wet presscakes in which the solid content is in the range of approximately 40 to approximately 60 percent of the total weight of the wet presscake..When presscake containing the preferred proportion of solids (40 to 60 percent) is used, one to eight molecular equivalents of anhydrous sodium sulfate for each ten molecular equivalents of water in the presscake is sufficient to obtain compositions of the invention having the preferred concentrations (35 to 70 percent) of active whitening agent specified above.

In a more specific embodiment of the first process aspect, this invention comprises treating a presscake consisting essentially of water and relatively large unground crystals of a fluorescent whitening agent by grinding said presscake at a temperature of 20 to 60 C. in the presence of one molecular equivalent of anhydrous sodium sulfate for each ten molecular equivalents of water in said presscake until substantially all of said crystals are reduced to a diameter of less than approximately five microns. Thus, a mixture of approximately one molecular equivalent of anhydrous sodium sulfate per each ten molecular equivalents of water in the presscake, as determined by routine analytical procedures is during the initial stages, either heated, or allowed to heat spontaneously, by virtue of friction and the heat of hydration of sodium sulfate, to a temperature within the range 35 to 60 C. (that is, above the melting point of sodium sulfate decahydrate, 32.4 C.), preferably about 50-60 C. At this stage, the mixture becomes a paste or dough-like mass consisting of fluorescent whitening agent dispersed in molten sodium sulfate decahydrate. The mixture is then allowed to cool to approximately 33 C. (i.e., below the melting point of sodium sulfate decahydrate) and the mixture is ground at this temperature for from one-half to two hours, depending upon the size of the batch, the original size of the crystals of fluorescent whitening agent, and the nature of the particular fluorescent whitening agent being processed. The temperature of the mixture is then allowed to fall to room temperature and the resulting dry, free-flowing powder consisting of finely comminuted fluorescent whitening agent dispersed in crystalline sodium sulfate decahydrate is collected.

The nature of the grinding apparatus is not critical in carrying out the processes of my invention, but I ordinarily prefer apparatus which is capable of exerting a shearing action on the relatively stiff pasty material and thus grinds the fluorescent whitening agent efficiently in the presence of the sodium sulfate as a grinding aid. An example of an efficient apparatus for this purpose is a dough mixing machine commonly called a flusher fitted either with a sigma-type blade or a dispersion blade. The dough mixing machines are commonly jacketed and can be heated or cooled as desired.

I have also found that a two-roll mill in which the rolls rotate at different rates affords an excellent means of grinding the mixture with the highly desirable shearing action. Particularly advantageous for grinding the mixtures are two-roll mills which have rotation ratios in the range of 1:1.1 to 1:1.25 and which can be made to exert separation forces in the range 1000 to 2000 pounds per linear inch.

When a two-roll mill is employed as the grinding apparatus in the process of this invention, the water-wet presscake and the anhydrous sodium sulfate are first intimately mixed or blended. The mixing is carried out in any conventional mixing or blending apparatus such as, for example, a fiusher as described above or a ribbonblender. The mixing is continued only long enough to insure complete blending and the mixture is then passed directly on to the two-roll mill. After passing through the mill, the composition is either pulverized directly or if desired is first dried and then pulverized.

It will be apparent that the compositions of this invention obtained as described above, by converting a waterwet presscake to a free-flowing granu ar P der, re ins substantially all the water from the presscake. Thus, when one molecular equivalent of anhydrous sodium sulfate is employed for each ten molecular equivalents of water in the presscake, the water is present in the final composition in the form of sodium sulfate decahydrate. For economic considerations and for some applications it is sometimes desirable to utilize substantially dry fluorescent whitening compositions and in these instances the compositions of this invention obtained as described above can be subjected to conventional drying techniques known to the art, for example oven-drying or flash-drying to remove either some or all of the moisture content with substantially no deleterious effects on the color or effectiveness of the compositions. I have found that compositions in a state of complete dryness tend to absorb small quantities of moisture from the'atmosphere and equilibrate in a range of approximately one-half to one and a half percent moisture content. The compositions dried to less than two percent are particularly preferred because in addition to possessing the excellent qualities previously noted, they also have excellent storage properties ordinarily encountered in commercial use.

The new processes of this invention are particularly adapted to treatment of any of the numerous fluorescent whitening agents employed in commercial detergents and fabric softeners thereby to produce compositions with the improved characteristics as herein indicated. For example, the following compounds, useful as fluorescent whitening agents, are effectively dried and comminuted by my new process:

Disodium 4,4-bis (4,6-dianilino-s-triazin-2-ylamino)-2,2'-

stilbenedisulfonate Disodium 4,4-bis (4-anilino-6-morpholino-s-triazin-2- ylamino)-2,2-stilbenedisulfonate Disodium 4,4'-bis(4-anilino-6-[2,2-dihydroxyethylamino]-s-triazin-2-ylamino)-2,2'- stilbenedisulfonate Disodium 4,4'-bis(4-anilino-6-[2-hydroxyethylamino]-striazin-Z-ylamino -2,2'-stilbenedisulfonate Sodium 2-(4-stilbyl) -naphtho[ 1,2 4,5] -1,2,3-triazole-2- sulfonate In contrast to the compositions of this invention, fluorescent whitening agents heretofore have been used in commerce either unground or ground in any of a number of common impact-type mills, for example, a hammer mill. Commercial fluorescent whitening agents produced by these known processes commonly average fifteen microns or more in their largest dimension. Efforts to reduce the size of these crystals further have heretofore yielded a product which is much too yellow in color to have value for use in modern detergents.

The composition according to the third composition aspect of the invention contains from approximately 35 to approximately 70 percent by weight of sodium sulfate decahydrate and from approximately 65 to approximately 30 percent by weight of dry fluoroescent whitening agent in finely divided form. This composition is characterized as a white to yellowish-white free-flowing powder which is readily soluble or dispersible in water or aqueous soap or synthetic detergent solutions.

The compositions provided by this invention are useful as optical whitening and brightening agents, particularly when incorporated into solid detergent or soap compositions, liquid detergent formulations and textile softeners. They are also useful for whitening and brightening textiles and paper in the absence of detergents in accordance with procedures well known to the art. A decided advantage of the compositions of this invention over those of the prior art is the high degree of water solubility of the fluorescent whitening agent, even in cold water. Moreover, more efficient whitening is accomplished by the use of these compositions because of their improved solubility characteristics over the same compounds obtained in accordance with known methods.

The following examples serves to further illustrate the invention without limiting the latter thereto.

EXAMPLE 1 1 A one-gallon laboratory flusher (dough mixer), fitted with a sigma-type blade and a heating and cooling jacket, was charged with a 1035 g. presscake of disodium 4,4- bis(4 anilino 6 morpholino-s-triazin-Z-ylamino)-2,2'- stilbenedisulfonate containing 73 percent solids [766 g. of fluorescent Whitening agent and 260 g. (14.9 moles) of water]. Anhydrous sodium sulfate (206 g.; 1.45 moles) was added, while mixing was continuously maintained, and then the mixture was heated to 55 C. When the mass became paste-like, the temperature was lowered to 33 C., and the mixing was continued for one hour. The mixture was then cooled to 28 C., whereupon the paste-like mass solidified and was broken up by the blades into a line granular powder. There was thus obtained 1172 g. of product which contained approximately 65 percent of disodium 4,4 bis(4 anilino-6-morpholino-s-triazin-Z-ylamino)-2,2'-stilbenedisulfonate and approximately 35 percent sodium sulfate decahydrate. Examination of this product under the microscope showed that the fluorescent whitening agent existed as broken crystals averaging three microns in their largest dimension.

The rate of solution of the above-described composition in water was determined by continuously measuring the fluorescence of a solution of the composition in contact with a weighed sample of the product. The fluorescence was measured on a Turner 'Fuorometer (G. K. Turner Associates, Palo Alto, -Calif.). Following are the data obtained, comparing the rate of solution of the above described composition of this invention with standard disodium 4,4-bis(4 anilino 6 morpholino-s-triazin-Z- ylamino)-2,2-stilbenedisulf0nate dried and ground in the conventional manner. The crystals of the standard (Std.) were needles or rods which had been ground in an impact-type grinding apparatus to an average size of -15 microns in length, according to the usual commercial procedure.

There data show that the composition of Example 1 dissolved approximately twice as rapidly as did the standard fluorescent whitening agent. The sample also showed approximately percent stronger dyeing of cotton cloths after five and ten minute washing cycles than did the standard fluorescent whitening agent.

Detergent compositions incorporating the composition of Example 1 were prepared and were measured for color grade on a Hunterlab Model D25 Color and Color-Difference Meter (Hunter Associates Laboratory, Inc., Fairfax, Va.), in accordance with the general method described in the Journal of the Optical Society of America, 48, 985 (1958). The above-described composition was found to be within the range of color specifications required for use in detergent powders and much whiter, pinker and bluer than the standard fluorescent whitening agent which had been ground to equivalent particle size in the absence of sodium sulfate.

EXAMPLE 2 A laboratory blender (Kitchenaid Model KS-A manufactured by the Hobart Mfg. Co., Troy, Ohio) was charged with a 700 g. presscake of disodium 4,4-bis(4-anilino-6- morpholino-s-triazin-2-ylamino)-2,2' stilbenedisulfonate containing 68.8 percent solids [481 g. of fluorescent whitening agent and 219 g. (12.2 moles) of water].

Anhydrous sodium sulfate (481 g.; 3.39 moles) was added, while mixing was continuously maintained at room temperature. After approximately ten minutes, mixing was stopped and the powder-like mixture was passed through a two roll mill at room temperature. The two roll mill (manufactured by Reliable Rubber and Plastic Equipt. Mfg. Co., North Bergen, NJ.) having two rolls six inches in diameter and thirteen inches in length, which rotate in a ratio of approximately 1:1.25, was set to exert separating forces in the range of 1000 to 2000 pounds per linear inch. The milled mixture was then dried in an oven at -110 C. to a constant weight and was finally passed through a pulverizing machine (Mikro Pulven'zcr Type CF, manufactured by Pulverizing Machinery Div., Metals Disintegrating Inc., Summit, NJ.). The fine granular powder thus obtained contained approximately 51 percent of disodium 4,4'abis(4-anilino-6-morpholinostriazin-Z-ylamino)-2,2'-stilbenedisulfonate and approximately 49 percent anhydrous sodium sulfate. Examination of this product under the microscope showed that the fluorescent whitening agent existed as broken crystals averaging less than three microns in their largest dimension.

The rate of solution of the above-described composition in water was determined by following the same procedure described in Example 1 above.

These data show that the composition of Example 2 dissolved in approximately one-third the amount of time as did the standard fluorescent whitening agent. This sample also exhibited approximately 25 percent stronger dyeing of cotton cloths after five and ten minute washing cycles than did the standard fluorescent whitening agent.

Detergent compositions incorporating the composition of Example 2 were prepared and measured for color grade in accordance with the test procedure described in Example 1. The composition of Example 2 was found to be within the range of color specifications required for use in detergent powders and was found to be much whiter, pinker and bluer than the standard fluorescer whitening agent which had been ground to equivaleL particle size in the absence of sodium sulfate.

I claim:

1. A fluorescent whitening composition consisting essentially of approximately 65 to approximately 30 percent of a crystalline fluorescent whitening agent having a particle size less than approximately five microns selected from the group consisting of disodium 4,4 bis(4,6- dianilino s triazin 2 ylamino) 2,2 stil benedisulfonate, disodium 4,4-bis(4anilino-6-morpholino-s-triazin- 2-ylamino) 2,2 stilbenedisulfonate, disodium 4,4- bis(4 anilino 6 [2,2 -pdihydroxyethylamino] s triazin 2 ylamino) 2,2 stilbenedisulfonate, disodium 4,4 bis(4-anilino 6 [2 hydroxyethylamino] -s-triazin- 2 ylamino) 2,2 stilbenedisulfonate and sodium 2-(4- stilbyl) naphtho[1',2:4,5] 1,2,3 triazole-Z-sulfonate and, in admixture therewith, approximately 35 to 70 percent by weight of crystalline sodium sulfate decahydrate.

2. A fluorescent whitening composition according to claim 1, wherein the fluorescent whitening agent is disodium 4,4 bis(4 anilino 6 morpholino s triazin- 2-ylamino)-2,2'stilbenedisulfonate.

3. A fluorescent whitening composition having a moisture content of less than two percent consisting essentially of approximately 35 to approximately 70 percent by weight of a crystalline fluorescent whitening agent having a particle size less than approximately five microns selected 7 from the group consisting of disodium 4,4 bis(4,6- dianilino s triazin 2 ylamino) 2,2 stilbenedisulfonate, disodium 4,4-bis(4 anilino 6 monpholino-striazin 2 y1amino)'- 2,2 stilbenedisulfonate, disodium 4,4 bis(4 anilino 6 [2,2 dihydroxyethylamino] -s- 5 triazin 2 ylamino) 2,2 stilbenedisulfonate, disodium 4,4 bis(4 anilino-6-[Z-hydroxyethylamino]-s-triazin-2- ylamino)-2,2'-stilbenedisulfonate and sodium 2-(4-stilby1)- naphtho[1',2':4,5]-1,2,3-triazole-2-sulfonate and, in admixture therewith, approximately 65 to 30 percent by weight of anhydrous sodium sulfate.

4. A fluorescent whitening composition according to claim 3, wherein the fluorescent whitening agent is disodium 4,4 bis(4 anilino 6 morpholino s triazin- 2 ylamino) 2,2 stilbenedisulfonate.

8 References Cited UNITED STATES PATENTS 2,654,713 10/1953 Fleck 252301.3 W 3,630,944 12/1971 Ohkawa et a1. 252-3012 W DANIEL E. WYMAN, Primary Examiner A. P. DEMERS, Assistant Examiner US. Cl. X.R. 

